Trouble soldering bare a123 batteries

[fishingpaul]

After breaking apart some old a123 cells I cannot solder new tabs to them,looking on other forums it seems a common problem,i have tried a very good quality large head soldering iron but the tabs still come apart,i was thinking of putting them in a straight line in a plastic tube, with springs between them instead of soldering,do you think this would work ok.

 

[Deleted member 4366]

The springs would have to be thick to carry the current without heating up. Spot-welders are about £100.

 

[fishingpaul]

Thanks d8veh I'm trying to do a cheap fix so a spot welder is a no go,how thick do you think the springs would have to be.

 

[D8ve]

Ribbon springs . Basically a flat strip folded into a v or w form. But the issue is the losses mount up every joint increases resistance and that wastes energy as heat in battery reducing your range.
Special spot wielders are cheap at £100, this isn't a no money game. You need some to get a working system.

 

[Deleted member 4366]

steel wire has about 50 times the resistance of copper. 16g steel wire has a resistance of about 0.15 Ohms per foot. You'd need about 2ft, so say 0.3 Ohms total. Multiply that by the number of amp your controller allows, double it to allow for contact resistance, and that'll give you the power dissipated. That means with a 15A controller, it's 4.5 watts.

 

[anotherkiwi]

The other day I came upon specialised spot welders that do 18650 cells and... lipo pouch tabs! $280 delivered. A cottage industry idea immediately sprang to mind.

 

[fishingpaul]

Thanks for the replys,the batteries are at least five years old,and have been used and abused by me,not realising I had a couple of dead cells they have been overcharged at least a couple of times,although still reading 3.2 to 3.5 volts per cell,i am not going to spend £100 on a spot welder,for what could be a very short lived battery,if only id have read about the soldering problems before I broke the tabs off them.